Fluid bearing operable in a vacuum region

ABSTRACT

A fluid bearing suitable for use in a vacuum region comprises a fluid passageway for introducing a fluid into the bearing, a pump-out slot for evacuating the fluid from the bearing, and a bearing seal disposed along a periphery of the bearing to restrict fluid from escaping from the bearing into the vacuum region. The bearing seal comprises a bridge structure including a first base, a second base, a transverse member fixed at one end to the first base and movably disposed in a slot defined by the second base, and a sealing sheet extending from the transverse member between the first and second bases. The sealing sheet forms a compliant mechanical wall around the periphery of the bearing. The seal further includes an adjustable spring force element which exerts a force on the sealing sheet to ensure marginal contact with a bearing support surface to form a low-frictional seal. The sealing sheet confines the fluid which escapes outside of the pump-out slots to within the perimeter of the wall formed by the sealing sheet. The seal allows for movement of the air bearing relative to the bearing support surface and is suitable for use with an XY wafer or reticle stage. The air bearing and its seal may be adapted as a journal shaft-type bearing.

FIELD OF THE INVENTION

This invention relates generally to stage devices for precision movementand location, such as used in lithography systems, and moreparticularly, to a fluid bearing with seal operable within a vacuumsystem.

BACKGROUND OF THE INVENTION

The precise positioning of an object is required in many applications,including lithography processing in semiconductor manufacturing forforming integrated circuits on semiconductor wafers. As the circuitdensity of integrated circuits increases and feature size decreases, theaccuracy in the methods for laying down the circuits on thesemiconductor wafer must improve. Various systems and methods have beendeveloped to attempt to improve positioning and movement of asemiconductor wafer in the lithography process. One way to increase theaccuracy is to reduce system complexity and size of the stage device,thus providing greater stability of motion during positioning of thewafer.

Air bearing systems are often used to provide smooth and accuratemovement between a stage and another planar surface or a guidestructure. An example of a stage device for use in semiconductorprocessing equipment is disclosed in U.S. Pat. No. 5,760,564. The stageassembly includes two guide rails, one movable in the X direction andthe other movable in the Y direction. A plurality of air bearings areattached to the guide rails and stage for movement of the guide railsand stage relative to the base. Since the bearings are attached to thestage and travel with the stage, the base must be at least as large asthe diameter of the bearing plus the entire stroke (travel) of thestage. This results in a large base and stage.

Examples of air bearing systems include differentially pumped airbearing systems such as those disclosed in U.S. Pat. No. 4,191,385 toFox and U.S. Pat. No. 4,425,508 to Lewis et al.. Lewis et al. disclosean air bearing intended for use in a vacuum chamber, such as in anelectron beam lithography system. The air bearing includes an airbearing plate defining a plurality of H-shaped grooves around its outerperiphery and a metering valve disposed in each H-groove for introducingpressurized air into each H-groove. The pressurized air provides an aircushion between the face of the air bearing plate and the opposing faceof a moving plate. The air bearing plate also includes a central vacuumregion circumscribed by two concentric pump-out slots. The pressure inthe vacuum region is maintained by conventional vacuum pumps. The twoconcentric pump-out slots are radially inward of the H-grooves toscavenge the air escaping inwardly from the H-grooves in order toprevent the air from reaching the vacuum region. Thus, the pump-outslots separate the air bearing from the central vacuum region.

Air from the air bearing flows through the small gap between the airbearing plate and the opposing face of the moving plate. Small valuesfor the gap are required in an attempt to reduce air flow to the vacuumregion. However, the smaller the gap, the tighter the necessarymechanical tolerance on the air bearing plate and the opposing surfaceof the moving plate, substantially increasing the manufacturing costs. Atypical air bearing gap is approximately 5 microns, requiring precisionmachining over a relatively large surface area to substantially increasemanufacturing costs, particularly because two such large precisionmachined surfaces are needed. In addition, because the stiffness of theair bearing is a function of this gap, adjusting the gap purely tocontrol the air flow is often impractical.

Thus, it is desirable to provide an air bearing which is effective inpreventing gas leakage into the vacuum environment and which is suitablefor use within a vacuum environment and not just surrounding a vacuum.It is further desirable to provide such an air bearing which is costeffective, simple to manufacture, robust, and which produce very littlewear or vibration during operation.

SUMMARY OF THE INVENTION

The air or other fluid bearing of the present invention suitable for usein a vacuum region comprises a bearing structure defining pump-out slotsor passageways circumscribing a central fluid bearing outlet. One ormore bearing seals are disposed along a periphery of the bearing to forma sealing wall. The sealing wall confines the fluid which escapedoutside of the pump-out slots to within the perimeter of the wall formedby the sealing sheet and prevent the escape of fluid into thesurrounding vacuum region. The bearing seal comprises a bridge structureincluding a first base, a second base, a transverse member fixed at oneend to the first base and movably disposed in a slot defined by thesecond base, and a sealing sheet extending from the transverse memberbetween the first and second bases.

The sealing sheets may but need not contact the opposing bearingsurface. Even if there is a gap between the adjacent sealing sheets andbetween the sealing sheets and the opposing bearing surface, the sealingsheet structure serves to prevent nearly all of the gas molecules fromescaping into the surrounding vacuum region and the gas molecules areeventually evacuated through one of the pump-out slots. The sealing wallstructure may be fabricated using semiconductor type processingtechnology from, for example, silicon or thin metal films to providing alight flexible structure.

The seal further includes an adjustable spring force element, such as aspring, a constant force spring, or a flexural coupling, which exerts aforce on the sealing sheet to ensure marginal contact with a bearingsupport surface to form a low-frictional seal.

The sealing sheet wall of the inventive bearing exerts a relatively lowfrictional force on a surface of a stage movable relative to the bearingso as to not impede the motion of the stage. The low frictional force isa result of both the relatively low mass of sealing sheet and the gap,if any, between the sealing sheets and the opposing bearing surface.Thus, the bearing of the present invention provides fast and precisemovement and positioning while maintaining the vacuum surrounding theair bearing. In addition, a plurality of individual air bearings of thepresent invention may be utilized within a vacuum region.

The air pressure at the outer pump-out slots is preferably sufficientlylow such that the air is in the molecular regime in that the molecularmean free path is much greater than mechanical system dimensions.Accordingly, the sealing sheets may be very light as the forces exertedby the impinging gas molecules against the sealing sheet structure arenegligible.

The seal allows for movement of the air bearing relative to the bearingsupport surface and is suitable for use with an XY wafer or reticlestage. The air bearing and its seal may be adapted as a journalshaft-type bearing.

The bearing of the present invention is most appropriately applicable togas bearings. The bearing of the present invention can be advantageouslyapplied to fluid bearings if the bearing is designed to providesuccessful scavenging of the fluid, similar to the gas bearing describedabove. In a fluid bearing, some fluid vapor will typically remain andits pressure is generally related to the vapor pressure of the fluid.Vapor pump-out slots may be provided to reduce the vapor pressure withinthe air bearing and the sealing sheet structure can reduce the vaporpressure in the vacuum system to a tolerable level.

The above is a brief description of some deficiencies in the prior artand advantages of the present invention. Other features, advantages, andembodiments of the invention will be apparent to those skilled in theart from the following description, drawings, and claims. Correspondingreference characters in the drawings indicate corresponding partsthroughout the several views of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bottom plane view of a fluid bearing system of the presentinvention;

FIG. 2 is a cross-sectional view of the fluid bearing system of FIG. 1along line 2—2;

FIGS. 3 and 4 each shows an enlarged partial cross-sectional view of thefluid bearing of FIGS. 1 and 2 illustrating the bearing seal in greaterdetail;

FIG. 5 is a partial side cross-sectional view of the fluid bearingsystem along line 5—5 of FIG. 3;

FIG. 6 is a cross-sectional side view along line 6—6 of a base member ofthe fluid bearing of FIG. 4;

FIG. 7 is a partial side cross-sectional view of an alternativeembodiment of the fluid bearing system of the present invention;

FIG. 8 shows an enlarged partial cross-sectional view of the fluidbearing of FIG. 7 illustrating the fluid bearing seal in greater detail;

FIG. 9 is a cross-sectional view of a journal shaft-type fluid bearingutilizing a fluid bearing of the present invention adapted for use as ajournal type bearing; and

FIG. 10 is a enlarged view of the portion of the portion of FIG. 9included within the circle 10.

DESCRIPTION OF THE INVENTION

The present invention comprises a bearing suitable for use in a vacuumenvironment such as to support a stage which holds a semiconductor waferbeing scanned by an electron beam lithography machine or otherlithography systems. The following description is presented to enableany person skilled in the art to make and use the invention.Descriptions of specific applications are provided only as examples.Various modifications to the preferred embodiment will be readilyapparent to those skilled in the art, and the general principles definedherein may be applied to other embodiments and applications withoutdeparting from the spirit and scope of the invention. Thus, the presentinvention is not intended to be limited to the embodiments shown, but isto be accorded the widest scope consistent with the principles andfeatures described herein. Copending U.S. application Ser. No.09/012,432, filed on Jan. 23, 1998, entitled “Air Bearing Operable in aVacuum Region” by Michael R. Sogard and Dennis Spicer, discloses thedesign of an air bearing operable under vacuum conditions for use withan X-Y stage used in a vacuum chamber, for example. The entirety of U.S.application Ser. No. 09/012,432 is incorporated herein by referencethereto.

Although the fluid bearing of the present invention is generallydescribed below as an air bearing, it is to be understood that thebearing of the present invention can be adapted for use as a fluidbearing.

FIG. 1 is a bottom plane view of a fluid bearing 20 of the presentinvention and FIG. 2 is a cross-sectional view of the bearing 20 alongline 2—2 of FIG. 1. The bearing 20 generally comprises a structuredefining a passage 22 terminating in a small orifice 24 which opposes asurface of the substrate 26 interfacing with the bearing 20. The bearing20 may support an XY stage (not shown) on its top surface, for example.The air bearing 20 is preferably movable in a plane over the planaropposing surface of the substrate 26.

A small gap (not shown) is maintained between the opposing surfaces ofthe bearing 20 and the substrate 26. The gap is preferably approximately5-10 μm. Pressurized air or other suitable fluid is introduced from aconventional source into the air bearing 20 via passage 22. The fluidexits through orifice 24 and is radially distributed through the gapbetween the bearing 20 and the substrate 26. A plurality of passagesand/or orifices may be provided. Alternative ways of introducing fluidto the bearing may be provided. For example, the bearing 20 may provideslots in a porous region through which fluid may diffuse.

The bearing 20 further defines two circular pump-out slots 28, 30concentric with orifice 24 for evacuating the fluid from the bearing 20.The pump-out slots 28, 30 are in fluid communication with portions 32,34, respectively, of a pump-out manifold. Alternatively, the bearing 20may provide one or more than two pump-out slots. Preferably,differential vacuum pressures are applied to manifold portions 32, 34.In particular, a higher vacuum is applied at the outer pump-out slot 30than at the inner pump-out slot 28. Further, in the case of an airbearing, because the input air to the bearing 20 is typically suppliedat a pressure higher than 1 atmosphere, bearing 20 may provide aseparate slot (not shown) radially inward of the pump-out slots 28, 30to allow the air to escape to the ambient air surrounding the vacuumsystem. The provision of such a separate pump-out slot in fluidcommunication with the ambient surrounding the vacuum system facilitatesin reducing the pumping requirements for the pump-out slots 28, 30.Additionally, the fluid pressure distribution within the bearing isidentical to that of the bearing operating under normal atmosphericconditions. Thus, performance of the bearing can be predicted based onthat of similar conventional bearings.

Preferably, the levels of vacuum applied by the pump-outs are such thatthe fluid immediately radially outside the outer pump-out slot 30between the bearing 20 and substrate 26 is in molecular regime such thatthe localized fluid pressure is very low. However, the fluid pressure atthis point may nonetheless be higher than the pressure in the vacuumenvironment exterior of the bearing 20. Thus, it is desirable to furtherprevent or minimize the gas from escaping into the surrounding vacuumregion. Thus, bearing 20 further comprises one or more bearing seals 40disposed around, for example, a perimeter of the bearing 20.

The bearing seals 40 are shown in more details in FIGS. 3-6. FIGS. 3 and4 each shows an enlarged partial cross-sectional view of the bearing 20.FIG. 5 is a partial side cross-sectional view of the bearing systemalong line 5—5 of FIG. 3. Although the bearing seals 40 are shown inFIG. 1 to be disposed at the periphery of the bearing 20, the bearingseals 40 may be disposed in any suitable configuration within theperiphery of the bearing 20 and radially outward of the outer pump-outslot 30.

Each bearing seal 40 generally comprises a bridge structure extendingfrom supports 36, 37. The bridge structure includes a first base 42, asecond base 44, a transverse member 46 coupled to the first base 42 andslideable within the second base 44, and a sealing sheet 48 extendingfrom the transverse member 46. The transverse member 46 extends betweenthe first and second bases 42, 44 and is fixed at one end to the firstbase 42 and movably disposed in a slot 50 defined by the second base 44,as will be described in more detail below. The transverse member 46 maybe affixed to the first base 42 by any suitable mechanism such as a setscrew, adhesive, welding, or may be integrally formed. The mechanismmust be vacuum compatible, however. The first and second bases 42, 44are preferably disposed such that there is a clearance between the bases42, 44 and the opposing surface of the substrate 26. For example, theclearance may be approximately 0.1-0.5 mm. This clearance avoids theneed for the tight mechanical tolerances demanded by the bearingsurfaces themselves.

The sealing sheets 48 of the bearing seals 40 together form a wall withsmall gaps between the adjacent sealing sheets 48 around the peripheryof the bearing 20 as shown in FIG. 1. Alternatively although notpreferred, the bearing seals 40 may be integrally formed on each side ofthe bearing 20. For example, in the embodiment shown in FIG. 1, thebearing 20 may comprise four bearing seals 40, one on each of the foursides of the bearing 20. In another alternative embodiment, the bearingseals 40 may be integrally formed such that the sealing sheet forms asingle integral wall around the outer pump-out slot 30.

The wall formed by the sealing sheets 48 confines the fluid escapingoutside of the pump-out slots 28 and 30 to within the perimeter of thewall. The sealing wall formed by the sealing sheets 48 thus provides ahigh level of containment of the gas or fluid in the air bearing 20.Because the fluid pressure exterior to the outer pump-out slot 30 may beso low that the fluid may be in the molecular regime, the mean free pathof the molecules is larger than the dimensions of the gaps betweenadjacent sealing sheets 48 and the gaps, if any, between the adjacentsealing sheets 48 and the surface of the substrate 26. Thus, the amountof gas or fluid escaping past the inner and outer pump-out slots 28, 30and through the gaps of the bearing 20, such as between adjacent sealingsheets 48, would be extremely small.

The bearing seal 40 further comprises an adjustable spring force element52 which exerts a small force on the transverse member 46 which in turnsexerts a small force on the sealing sheet 48. The spring force or thespring constant of the spring force element 52 may be adjusted by anysuitable mechanism. The desired spring force of the spring force element52 may depend on the application and various parameters such as the sizeof the bearing 20 and the intended gap between the bearing 20 and theopposing bearing surface.

The spring force element 52 may provide a screw or other mechanism foradjusting the tension or spring constant of the spring element 52. Thesealing sheet 48 may be in marginal contact with the surface of thesubstrate 26 to form a low-frictional seal. Preferably, the adjustablespring force element 52 is adjusted to have a weak spring constant suchthat the frictional force exerted by the sealing sheet 48 on thesubstrate 26 as the bearing structure 20 moves relative to the substrate26 is small or negligible. Alternatively, the sealing sheet 48 may nottouch the surface of the substrate 26 and the sealing sheet 48 may“bounce” along slight irregularities on the surface of the substrate 26as the bearing 20 moves relative to the substrate 26.

The spring force element 52 advantageously allows the sealing sheet 48to move in the axial Z direction of the spring force element 52, forexample, due to thermal expansion and/or other axial motions of thesealing sheet 48 while maintaining marginal contact or close proximitybetween the sealing sheet 48 and the substrate 26. Thus, the bearingseal 40 allows for ease of movement of the bearing 20 relative to thesurface of the substrate 26.

The support 37 preferably defines a channel or an opening 38therethrough. The channel 38 facilitates pressure equilibrium betweenregion 39 and a region between the transverse member 46 and thesubstrate 26 radially interior of the sealing sheet 48. By providingthis pressure equilibrium mechanism, transverse member 46 need notsupport significant pressure differentials between region 39 and theregion between the transverse member 46 and the substrate 26 radiallyinterior of the sealing sheet 48. Alternatively, the support 37 may be aporous member to allow fluid to pass therethrough to achieve the desiredpressure equilibrium.

Sealing sheet 48 may be formed of, for example, a thin sheet of siliconor a compound of silicon or metal, mounted on a surface of thetransverse member 46. The sealing sheet 48 has an extremely small masssuch that very little force is needed to lift the sealing sheet 48 offof the opposing surface of the substrate 26. The small mass of thesealing sheet 48 ensures that wear, particle generation and mechanicalvibration when the bearing 20 moves relative to the substrate 26 areminimized. Where the sealing sheet 48 is formed of silicon or a siliconcompound, the sealing sheet 48 preferably has a thickness ofapproximately 50 to 1000 microns.

The first and second bases 42, 44, transverse member 46 and/or thesealing sheet 48 may be integrally formed of, for example, silicon, asilicon compound or metal. Well known semiconductor processingtechnology may be used to micromachine such structures. The fabricationof the first and second bases 42, 44, transverse member 46 and/or thesealing sheet 48 may be similar to that of cantilever probes used forinstance in scanning tunneling microscopy which can be fabricatedentirely from silicon or silicon compounds by micromachining. As anotheralternative, the transverse member 46 and the sealing sheet 48 may beformed by metal film deposition on a micromachined silicon substrate andmicromachining the resulting thin metal structure.

Furthermore, the contacting surface or tip of the sealing sheet 48 maybe coated with a thin layer of, for example, Si₃N₄, such that thesurface of the sealing sheet 48 will be much harder than many metalssuch that wear of the sealing sheet 48 can be negligible.

In one embodiment, the air bearing 20 is approximately 2″ by 2″.Multiple air bearings 20 of the present invention may be provided tosupport one or multiple stages. Each air bearing 20 can be individuallyisolated from the surrounding vacuum region.

FIG. 6 shows a cross-sectional side view of the second base 44 andsupport 37 of the bearing 20. The second base 44 generally comprises abody 54 defining the slot 50. As shown in FIG. 6, each slot 50 hascross-sectional dimensions slightly greater than those of the transversemember 46 such that the transverse member 46 can move slightly withinthe slot 50. Thus, by disposing a free end of each transverse member 46in the slot 50 of the second base 44, greater torsional strength andrigidity is imparted to the bearing seal 40. If the sealing sheet 48 andtransverse member 46 do not have sufficient torsional strength,irregularities on the surface of the substrate 26 may catch a comer ofthe sealing sheet 48, causing it to twist and possibly buckle and/orbreak the sealing sheet 48 or transverse member 46 when the bearing 20moves relative to the opposing surface of the substrate 26 in adirection generally parallel to one or more of the sealing sheets 48.

Because of the geometry of the transverse member 46 and because one endof the transverse member 46 is affixed to the first base 42 whileanother end is disposed within the slot 50, the transverse member 46generally cannot move laterally in any significant amount in the Ydirection. However, the provision of the slot 50 allows the transversemember 46, along with the sealing sheet 48, to move slightly in the Xdirection, the direction of the slot 50, as the height in the Zdirection of the bearing 20 relative to the substrate 26 varies. Inaddition, the provision of the slot 50 allows the transverse member 46,along with the sealing sheet 48, to twist about the X direction. Thesupport 37 forming a cover to the slot 50 may prevent the sealing sheet48 from twisting out of the slot 50. These features advantageouslyincrease the torsional rigidity of the bearing seal 40.

For example, when irregularities on the surface of the substrate 26catch a corner of the sealing sheet 48 as the bearing 20 is moving in adirection generally parallel to the sealing sheet 48, the slot 50 allowsthe transverse member 46 to move slightly in the X direction and totwist about the X direction. Such freedom of motion of the transversemember 46 thus imparts torsional rigidity to the sealing sheet 48.

FIGS. 7 and 8 are partial side cross-sectional views of an alternativebearing 120. The bearing seal 140 similarly comprises the bridgestructure including the first base 42, second base 44 defining a slot50, transverse member 46 coupled therebetween, and sealing sheet 48.However, in this embodiment, the spring force element is a flexuralcoupling 152. Similar to the embodiment described above, the springconstant of the flexural coupling 152 may be adjustable such as byproviding a screw for adjusting the tension of the flexural coupling152. Also, the desired spring force of the flexural coupling 152 maydepend on the application and various parameters such as the size of thebearing and the intended gap between the bearing and the opposingbearing surface.

Although the fluid bearing of the present invention is described interms of a fluid bearing for stages and which interfaces with anotherplanar surface, it is to be understood that the fluid bearing of thepresent invention is also applicable to, for example, a journalshaft-type fluid bearing where a round shaft is rotatable and/ortransversely slidable relative to the bearing, or a rectangular shaft istransversely slidable relative to the bearing, for example, as describedbelow. An application of such bearings is also described in M. Ohtsuka,SME International Journal, Series III, Vol. 33, 61 (1990), the entiretyof which is incorporated herein by reference.

For example, FIGS. 9 and 10 are cross-sectional views of a journalshaft-type bearing 70 utilizing a bearing of the present inventionadapted for use as a journal type bearing. In this embodiment, thejournal shaft-type bearing 70 is attached to an exterior surface of avacuum vessel wall 72, disposed outside a vacuum region defined byvacuum vessel wall 72 and about a shaft 74. For example, one end of theshaft 74 disposed outside of the vacuum region may be connected to amotor or other actuator to provide axial and/or rotational movement ofthe shaft and the other end of the shaft 74 disposed within the vacuumregion may be connected to a stage or other movable structure. Thevacuum region is also isolated from ambient air by the provision of avacuum O-ring seal 76. The shaft 74 is rotatable and/or slidablerelative to and within the concentric journal bearing 70.

Pressurized air or other suitable fluid is introduced from aconventional source into the air bearing 70 via passage 22′. The fluidexits from passage 22′ and is radially distributed in the gap betweenthe bearing 70 and the shaft 74. The bearing 70 further defines twopump-out slots 28′, 30′ concentric with shaft 72 for evacuating thefluid from the bearing 70. The pump-out slots 28′, 30′ are in fluidcommunication with portions 32′, 34′, respectively, of a pump-outmanifold.

The pump-out slot 30′ closer to the vacuum vessel wall 72 may reduce thepressure of the fluid to a molecular flow or near molecular flow regimeand a sealing wall formed by one or more bearing seals 40′ then reducesthe flow into the vacuum chamber to a level where a satisfactory vacuumlevel can be maintained without exorbitant pumping requirements.

As noted, the journal shaft-type bearing 70 comprises one or morebearing seals 40′. Similar to the previously described embodiments, eachbearing seal 40′ generally comprises a bridge structure including afirst base 42′, a second base 44′ (FIG. 10) defining a slot 50′, atransverse member 46′ coupled to the first base and slideable within theslot 50′ in the second base 44′, and a sealing sheet 48′ extending fromthe transverse member 46′. Each of these components is similar to thosedescribed above except that the sealing sheet 48′ has a curved edge toconform to the curved surface of the cylindrical shaft 74 and that thetransverse members 46′ of the bearing 70 are disposed about a circularperimeter of the shaft 74. The bearing seal 40′ also comprises anadjustable spring force element 52′ which exerts a small force on thetransverse member 46′ which in turn exerts a small force on the sealingsheet 48′. Where a gap exists in a radial direction between thetransverse member 46′ in the slot and a cover of the slot, thetransverse member 46′ and thus the sealing sheet 48′ is permitted totwist by a limited amount, thereby allowing the bearing seal 40′ toremain in contact with the shaft 74. This is so even if the shaft 74experiences eccentric motion and moves away from the center of thejournal when transverse forces are applied.

The bearing of the present invention provides an effective, reliable androbust yet simple, cost-effective, and space-efficient mechanism tocontain fluid within the bearing. For example, the bearing of thepresent invention allows greater tolerances between opposing surfaces ofthe bearing and the substrate, substantially decreasing manufacturingcosts.

While specific embodiments of the invention have been described andillustrated, it will be appreciated that modifications can be made tothese embodiments without departing from the spirit of the invention.Thus, the invention is intended to be defined in terms of the followingclaims.

What is claimed is:
 1. A fluid bearing assembly for bearing on a firstsurface, the assembly comprising: a structure having a bearing surfaceopposing the first surface, the structure defining: a fluid inputpassage terminating in the bearing surface and capable of directingfluid towards the first surface; a fluid output passage terminating inthe bearing surface and capable of directing fluid away from the firstsurface; and a seal comprising a transverse member having a free end, afixed end and a sealing sheet extending from said transverse memberbetween the free and fixed ends toward the first surface, the fluidoutput passage being disposed between the seal and the fluid inputpassage.
 2. The fluid bearing of claim 1, wherein said bearing structuredefines a perimeter, said seal being disposed adjacent said bearingstructure perimeter.
 3. The fluid bearing of claim 1, wherein the fluidoutput passage circumscribes the fluid input passage at the bearingsurface, and wherein the sealing sheet circumscribes the fluid outputpassage at the bearing surface.
 4. The fluid bearing of claim 1, whereinthe sealing sheet comprises silicon, silicon compound, or metal.
 5. Thefluid bearing of claim 1, wherein said bearing structure comprises aplurality of said seals and said sealing sheets of said plurality ofseals are disposed to form a sealing wall about the fluid output passageat the bearing surface.
 6. The fluid bearing of claim 5, wherein sealingsheets of said plurality of seals defines gaps therebetween in saidsealing wall.
 7. The fluid bearing of claim 1, wherein said seal furthercomprises a first base and a second base defining a slot therein, saidtransverse member fixed end is attached to said first base and saidtransverse member free end is disposed in said slot of said second base.8. The fluid bearing of claim 1, wherein said seal further comprises aspring force element coupled to said transverse member to exert a forceon said sealing sheet against the first surface.
 9. The fluid bearing ofclaim 8, wherein said spring force element has an adjustable springconstant.
 10. The fluid bearing of claim 8, wherein said spring forceelement is a flexural coupling.
 11. The fluid bearing of claim 1,wherein the first surface and said bearing surface are circular andwherein said sealing sheet has a curved edge to generally conform to aportion of the circular first surface.
 12. A method of sealing aninterface between a bearing structure and a surface, said methodcomprising: directing a flow of fluid to the surface through an inputchannel defined in the bearing structure; conducting the fluid away fromthe surface through an output channel defined in the bearing structureand exterior to the input channel on the bearing structure; andenclosing the fluid within a region between the surface and the bearingstructure by a sealing sheet disposed exterior to the output channel onthe bearing structure and extending toward the surface from a transversemember generally congruent with the surface, the sealing sheet extendingbetween a free end and a fixed end of the transverse member.
 13. Themethod of claim 12, further comprising maintaining a pressuredifferential between said region and another region exterior to saidregion.
 14. The method of claim 12, wherein in the region the fluid is agas having a pressure such that the gas is in the molecular regime. 15.The method of claim 12, further comprising moving the bearing structurerelative to the first surface.